Exhaust for a slant

Well I am gonna have some new exhaust put on my 70 duster with a 225. I need to know what are the best mufflers and pipe size? my plan right now is dual 2 1/2'' out the back with an x pipe and a good set of magnaflows with rectangle slant down tips. Also I have bored it 60 over with a new cam, bigger valves, .010 off the block and .080 off the head, offy dual one's and clifford headers. If anyone needs to know. Tell me if I have anything wrong in my thoughts.